One of the most moving stories to emerge during the 2012 Summer Olympics in London concerned “lost boy” runner Guor Marial.

A former refugee from the turmoil and civil war in Sudan in which eight of his brothers and sisters were killed, he ran a qualifying time for the Olympics in his first-ever marathon. The problem was that Mr. Marial had no country to run for. Instead, he ran under the Olympic flag.

Worcester native and documentary filmmaker Bill Gallagher was deeply touched when he read about Mr. Marial last year. “It’s hard for anyone to succeed in life, right? But for what he’s been through, it’s just incredible. He ended up being one of the elite runners in the world.”

Now, Mr. Gallagher is in the process of making a documentary about Mr. Marial with the working title of “Runner Without a Country.” Later in the year, he hopes to accompany Mr. Marial, 28, as he makes his first trip home — to what is now South Sudan — in 20 years.

Meanwhile, Mr. Marial and Mr. Gallagher will be at the Boston Marathon April 15. Mr. Marial had planned to run in the event, but a recent injury will force him to the sidelines. Still, he can at least meet a large contingent of fans still expected to be on hand from Concord, N.H., the place where he first discovered he could run competitively after coming to this country with an uncle. And after the marathon he will visit Concord to meet more friends.

After reading about Mr. Marial’s story last summer, Mr. Gallagher traveled to the London Olympics to meet him.

“I was struck by his humility and charm. He spoke of his running as something larger than himself,” Mr. Gallagher said.

“People thought the story ended in London, but it didn’t end there, and there was a lot more back-story.” So Mr. Gallagher broached the idea of a documentary.

“I thought it was a good idea,” said Mr. Marial in an interview last week. “I feel fortunate that I have someone like him to help me tell the story of what the South Sudan’s needs are.”

Part of Mr. Marial’s story includes being kidnapped as a child during the civil war and forced to do manual labor, fleeing a refugee camp, escaping with his uncle to Egypt, and settling in the United States. In Concord, he became a track star at high school, and then did the same thing at Iowa State University, where he was an All-American athlete. Mr. Marial, who is single, now lives in Flagstaff, Ariz., where he trains as a runner and tutors middle- and high-school students in math and science.

After qualifying for the marathon at last year’s Olympics, Mr. Marial faced a dilemma. The new nation of South Sudan, which he wanted to represent, hadn’t yet been recognized by the International Olympic Committee. Although he had lived in America several years, he was not yet an American citizen. But Sudan, the nation of his birth that South Sudan emerged from after a bloody conflict, did offer him a place on its team. Mr. Marial’s response was forthright: “If I ran for Sudan, I would be betraying my people.”

Many people petitioned the IOC on his behalf. Mr. Marial finished 47th in the marathon, with a time of 2:19:32.

His next full marathon was to have been the Boston Marathon, but he couldn’t overcome some tendinitis that also forced him to pull out of a recent New York City half-marathon event at the 10-mile mark.

On the bright side, Mr. Marial became a U.S. citizen in February, and also took dual citizenship with South Sudan. “It felt good,” he said.

Regarding which country he would represent in international competition if the opportunity arose, he said, “Most likely I would lean toward South Sudan. It’s been in my heart to do something for South Sudan, but it’s a very hard decision to make.”

He readily acknowledges he came here with nothing and the United States “lifted me.”

Mr. Marial said he runs in part to inspire refugees and for Americans to learn about South Sudan.

“It (South Sudan) still needs a lot — clean water, roads, hospitals, access to health care facilities. … It’s going to take time. It’s going to take sacrifice from each and every one including myself to move forward and help the next generation.”

“It’s going to be such an intense moment,” Mr. Gallagher said about the pending return journey to South Sudan. “They’re probably going to welcome him home like a hero.”

Mr. Marial said he is not sure what to expect. “I’ve been away a long time. I know I’m very excited. I have no idea right now what is going to happen. I have no idea.”

Mr. Gallagher was a producer and member of the small team that made the documentary “If a Tree Falls: A Story of the Earth Liberation Front” that was nominated for an Oscar last year. He grew up in the Quinsigamond Village section of Worcester, graduated from Holy Name Junior Senior High School and the University of Massachusetts at Amherst, and studied in the documentary program at The New School in New York. He previously worked for Marshall Curry Productions in New York, and is currently living in Spain (his fiancée is Spanish). “Runner Without a Country” would be Mr. Gallagher’s first documentary as a solo director.

Filming for it has already taken place in London, New York and Arizona. To help finance the project, Mr. Gallagher has just launched a campaign on Kickstarter, a website that tries to match artists and their projects with prospective backers. The initial goal is to raise $12,000. To visit the webpage, go www.kickstarter.com and search for “Runner without a Country.”

The campaign has already brought in more than $9,000, a good quick start. “That’s totally blown out my expectations,” Mr. Gallagher said.

He noted that many of the donations so far have come from people in Worcester. “I have a lot of good friends and family,” he said.